Adaptations

Question 1

what is an adaptation (noun)?

Answer 1

specialized features that enhance fitness

Question 2

what is an adaptation (verb)?

Answer 2

the process by which features that enhance fitness are fixed in a population or species

Question 3

what is crypsis?

Answer 3

implying that something can stay hidden/camouflaged

the ability of an animal to avoid observation or detection by other animals

it may be either a predation strategy or an anti predator adaptation

methods include camouflage, nocturnality, subterranean lifestyle, and mimicry

Question 4

what are some types of adaptations?

Answer 4

1) feeding specializations
2) crypsis
3) mate attraction or competition

Question 5

what are examples of mate attraction/competition?

Answer 5

• bright colors on male birds
• male to male combat with deer
• peacock feathers

Question 6

what qualifies something as an adaption?

Answer 6

adaptations MUST:
- improve fitness such that organisms WITH the trait have higher fitness than those without it

• show correlation between the presence of the feature and the hypothesized selective pressure –> does its presence correspond to a specific selective regime?

Question 7

True or False:

natural selection is the only known explanation for adaption

Answer 7

TRUE

natural selection leads to adaptations

drift can’t lead to adaptation because its random, it has nothing to do with organisms surviving or reproducing better

Question 8

True or False:

adaptations should be the result of evolution by natural selection

Answer 8

TRUE

Question 9

what is the relationship of causation between reproduction and fitness?

Answer 9

differential reproductive success and survival are the effect of differences in fitness

because of linkage among traits (pleiotropy) and passage of time, it can be complicated to evaluate WHAT selection has selected FOR (and thus it can be hard to determine whether something is an adaptation)

Question 10

what is pleiotropy?

Answer 10

linkage among traits

when one gene influences two or more seemingly unrelated phenotypic traits

Question 11

how can adaptations be identified?

Answer 11

by comparisons of related species specialized for different niches

Question 12

how long does it take for adaptation to occur?

Answer 12

adaptation is (usually) gradual

gradual evolution of complexity
ex. mollusk, eyeballs

Question 13

what is the gradual evolution of complexity?

Answer 13

Computer simulation (Nilsson & Pelger 1994)

• allowed eye parameters (shape, focal length, etc) to change by 1% per “mutation”
• required intermediates
• used quantifiable properties to measure the acuity of each model eye

Conclusion: it takes 400,000 generations to evolve complex vertebrate eye

Question 14

what is an analogous structure?

Answer 14

similarity due to convergent evolution, not common ancestry

• analogous structures have independent evolutionary origins –> the same type of adaptation can evolve more than once

functionally similar, but structural and historically different

ex. vertebrate eye and octupus eye
ex. bat wing and bird wing

• product of convergent evolution

Question 15

what is convergent evolution?

Answer 15

convergent evolution is the process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches

usually caused by similar selective pressures

ex. human and octopus eye
inverted retina causing blind spot vs. non-inverted with no blind spot

Question 16

what do similar selective pressures between species do?

Answer 16

they can cause convergent evolution

ABSENCE of selective pressure can also cause break-down and loss of pathways like animals that live in caves lose their eyesight and pigmentation

Question 17

what is a homologous structure?

Answer 17

traits inherited by two different organisms from a common ancestor

structural similar, but can be functionally different

ex. the pentadactyl limb is a mammalian homology
ex. dolphin’s flipper, bird’s wing, cat’s leg, and the human arm

• can be products of divergent evolution

Question 18

what is divergent evolution?

Answer 18

the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations allowing differentiated fixation of characteristics

Question 19

what is evidence for natural selection?

Answer 19

“poor design” is evidence for natural selection

The panda’s “thumb” is not homologous with
the human thumb…it is a makeshift adaptation for stripping bamboo that has evolved from a small bone in the wrist…not a “perfect” thumb

Question 20

what is the gardener’s dilemma?

Answer 20

when you are watering plants and walk around a tree and run out of hose, the sensible thing is to walk back around the tree

natural selection found another way by buying more hose and attaching it to the end to make the hose longer

Question 21

what is a real life example of the gardeners dilemma?

Answer 21

the male urogenital system

the vas deferens are the tube that carries the sperm from testicles to penis –> in cold blooded animals it lies deep within the body cavity –> for warm blooded animals this is bad because sperm is temperature sensitive so overtime the testes migrates out of the body cavity to the scrotum –> along the way the testes took a wrong turn past the ureter and the vas deferens got hooked there like the gardeners hose –> so instead of unhooking the vas deferens, selection just made it longer

not a great design but it works

Question 22

what are evolutionary anachronisms?

Answer 22

Evolutionary anachronism in plants, refers to those fruit, flower, leaf and stem attributes that evolved as an interaction with animals that are now extinct

many plants with large, tough seeds are not well adapted for seed dispersal at present because they depended on large herbivore dispersers that are now extinct

selective pressure changes!

Question 23

what are vestigial structures?

Answer 23

structures with little or no current function, retained due to common ancestry

ex. the emu, rhea, ostrich, and kiwi all have evolved to be flightless but still retain tiny, functionless wings

penguins are also flightless BUT their wings have adapted to a new habitat and have been modified for swimming

ex. humpback whales have pelvic bones
ex. lizard has eyes even though it can’t actually see

Question 24

what is pre-adaptation? (exaptation)

Answer 24

an existing feature contributes significantly to an increase in fitness when selective landscape changes

Question 25

what is preadaptation?

Answer 25

an existing structure modified to serve a new function

Question 26

what is exaptation?

Answer 26

an adaptation that has arisen via preadaptation

example:
original structure –> bird feathers for thermoregulation

new exaptation –> facilitates the evolution of flight

example:
original structure –> salivary glands in snakes used for digestion

new exaptation –> facilitates the evolution of venom

example:
original structure –> sweat glands for thermoregulation

new exaptation –> mammary glands for lactation

Question 27

what is the fitness landscape?

Answer 27

a significant shift in the phenotype might push organisms “off and over” the adaptive peak

the hills in the landscape are several possible “good” solutions to selective pressures but the hills are separated by valleys of “bad” solutions

Question 28

what are genetic constraints on adaptation?

Answer 28

heterozygote advantage: the form with the highest fitness can’t “breed true”

in crested newts, theres two variants of a chromosome, 1A and 1B –> only those individuals with one of each variant, 1A/1B heteromorphs survive, all homomorphs, 1A/1A or 1B/1B, die before birth –> in each generation, half of the reproductive effort is wasted because 50% of the offspring are homomorphs

Question 29

what are developmental constraints on adaptation?

Answer 29

developmental constraints: certain morphologies are impossible developmentally

the shape of a coiled shell can be described by three numbers: translation rate, expansion rate, distance from coiling axis

of all the possible shell shapes, only a small fraction are actually observed in nature

either these shell types have been consistently selected against or they are impossible to actually make because of some unknown developmental constraint

Question 30

what is allometry?

Answer 30

it’s a type of developmental constraint

something is allometric if it scales with size

in cervids, antler size is allometric –> a larger species will have not only an absolutely larger set of antlers but a relatively larger set of antlers

the extinct Irish Elk is thought to be near the developmental limit for antler/body size evolution because any further increase in body size would result in such a disproportionately large rack of antlers that it would exceed the weight that could be supported by the neck

Question 31

what are trade-offs

Answer 31

constraints on adaptation

trade-offs are where an adaptation for one function may compromise another function

ex. in cheetahs, longer legs are good because then the cheetah is faster but then bones get brittle faster, it’s a trade off
ex. in lizards they can have a few large eggs for fewer offspring or lots of small eggs with poor offspring survival –> so they can put energy into growth or reproduction –> so you can delay growth and grow slower and you live longer but then have few offspring

Question 32

what is the adaptive landscape?

Answer 32

Different solutions to the same problem –>  peaks are solutions and the “global peak” is the best solution out there 

natural selection is acted upon at a peak

you can argue that you’d never know what the global peak is

selection operates on existing variation and “chooses” the local peak, it probably will not cross a non-adaptive valley

ex. three different peaks are cephalopod lens eyes, mirror eyes, and vitreous mass eyes